In systems with multi-layered architecture, such as a system under the Open Systems Interconnection Model (“OSI”), where data transfer occurs in packets, data link layers such as Radio Link Control (“RLC”) and Medium Access Control (“MAC”) are not aware of the type of data being transmitted. Thus, even for IP Multimedia Subsystem (“IMS”) and other high priority data, data link layers follow the normal retransmission mechanisms. Yet, some data is time critical. For more time critical data, such as IMS call establishment, use of the normal retransmission mechanisms can lead to delay in call establishment, poor user experience, or call failure.
In circumstances where the Radio Access Technology (“RAT”) is unavailable for transmission of time critical data, the data plane bearers will generally not be advised about the unavailability of the RAT, and they will continue to attempt retransmissions to the physical layer. This results in repeated retransmission attempts, which can result in unacceptable latency for time critical data.